FWIW, here’s the response from Backblaze support:
“Extended attributes aren’t included in the backed up files. This means no finder comments, no finder tags, no quarantine information, and a few other items.
Permissions and modified dates are retained. Creation dates are technically backed up as well but they aren’t retained when restoring a file so they’re essentially not backed up as well.
You might also find modified dates to be changed to the date that files are restored via zip restore as certain zip utilities might set their own modified dates during the unzip process.
As for an encrypted database, it would indeed need to be accessible in order for it to be backed up.”